Discussion on the surge problem in centrifugal fans
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In many technical articles, the issue of surge in centrifugal fans is discussed. The hazards associated with surge are very serious, and it is known that fan surge occurs under specific operating conditions at low flow rates. Some classmates have also brought up this topic for discussion before, but I think it hasn’t been explored in enough depth. How can we prevent surge? What flow rate threshold should be maintained, or can the fan current be used as an indicator? Please discuss this.
Current does not indicate whether surge is occurring or not; it is characterized by the outlet pressure and inlet flow rate. There should be in-depth discussions on the forum; you can search for them and take a look.
Currently, the surge curves of fixed-speed fans are provided by the manufacturers after factory testing, or they can be calibrated on-site, or calculated using certain formulas. Here is a formula for reference: N0 = 3.5555 * 305 / (T0 + 273) * Q0 + 64.4445. Here, N0 represents the power under the fan’s operating conditions; T0 is the temperature at the fan’s inlet, and Q0 represents the power measured by electrical instruments. When N0 ≤ N, the PLC issues an alarm. This post was last edited by SDZBTG on 2009-3-11 at 11:28
Surge can be controlled using flow rate and pressure ratio, or using power and pressure ratio; if voltage is assumed to remain constant, it can be controlled using current and pressure ratio. The surge control line is a curve (or an approximate straight line); it is not possible to truly prevent surges using just one parameter. (Of course, by sacrificing efficiency and using a safe flow or current value, surges can be avoided, but this will prevent the machine from reducing its load and increase production costs.)
Surge is a specific issue related to the behavior of centrifugal compressors; it is a phenomenon of \"uncontrolled operation\" that occurs when the volume of air entering the compressor decreases to a certain level. When surge occurs, the machine vibrates violently and emits a roaring sound, resulting in extremely unstable operation. When a centrifugal compressor experiences surge, typical phenomena include: 1) the outlet pressure of the compressor first increases, then drops sharply, exhibiting periodic and significant fluctuations ； 2) The compressor’s flow rate drops sharply and fluctuates significantly; in severe cases, air even reverses flow back into the intake pipeline ； 3) The current and power meter readings of the compressor motor become unstable, with significant fluctuations ； 4) The machine experiences severe vibration, along with abnormal gas noises. Currently, there are three common methods to address surge: ① Adding bleed valves to the compressor to allow excess gas to be discharged. ②Use a twin-rotor or triple-rotor pneumatic compressor. ③Use adjustable blades.